1. Field of Invention
Embodiments disclosed herein relate generally to polycrystalline diamond constructions and cutting structures comprising the same and, more particularly, to methods and materials used for improving the thermal stability of polycrystalline diamond constructions and the polycrystalline diamond constructions resulting therefrom.
2. Background Art
Polycrystalline diamond compact (“PDC”) cutters have been used in industrial applications including subterranean drilling and metal machining for many years. In a typical application, a compact of polycrystalline diamond (PCD) (or other superhard material) is bonded to a substrate material, which is typically a sintered metal-carbide to form a cutting structure. PCD comprises a polycrystalline mass of bonded-together diamond grains or crystals that form an integral, tough, high-strength mass or lattice. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
PCD may be formed by subjecting a volume of diamond grains to certain high-pressure/high-temperature (HPHT) conditions in the presence of a sintering aid or binder. Conventionally, the sintering aid or binder is provided in the form of a solvent metal catalyst material, such as one or more element from Group VIII of the Periodic table. The solvent metal catalyst may be added and mixed with the diamond grains prior to HPHT processing and/or may be provided during the HPHT process by infiltration from a substrate comprising the solvent metal catalyst as one of its constituent materials.
A conventional PDC cutter may be formed by placing a cemented carbide substrate into a HPHT container. A mixture of diamond grains or diamond grains and catalyst binder is placed atop the substrate in the container and the container is loaded into a HPHT device that is configured and operated to subject the container and its contents to a desired HPHT condition. In doing so, the solvent metal catalyst material in the substrate melts and infiltrates into the diamond grain volume to promote intercrystalline bonding therebetween, thereby forming a sintered diamond body that is bonded to the substrate. The substrate often comprises a metal-carbide composite material, such as tungsten carbide. The deposited diamond body may be provided in the form of and referred to as a “diamond layer”, a “diamond table”, or an “abrasive layer.” The solvent metal catalyst material in such conventional PCD is disposed within interstitial regions that exist between bonded-together diamond crystals. Conventional PCD includes 85 to 95 percent by volume diamond and a balance binder or catalyst materials.
As noted above, PDCs are useful for forming cutting elements, e.g., PDC cutters, used in applications calling for high degrees of wear and abrasion resistance, such as drilling subterranean formations. A significant factor in determining the longevity of PDC cutters is the generation of heat at the cutter contact point, specifically at the exposed part of the PCD layer caused by friction between the PCD and the work material being engaged. This heat causes thermal damage to the PCD in the form of cracks (due to differences in thermal expansion coefficients), which lead to spalling of the PCD body or layer, and/or delamination between the PCD body and substrate, and/or back conversion of the diamond to graphite in the PCD body causing rapid abrasive wear. As a result, the thermal operating range of conventional PDC cutters is typically less than about 750° C.
Conventional PCD is stable at temperatures of up to about 700 to 750° C., after which observed increases in temperature may result in permanent damage to and structural failure of PCD. This deterioration in PCD is due to the significant difference in the coefficient of thermal expansion of the binder or catalyst material, e.g., as compared to diamond. Upon heating of PCD during use, the catalyst material and the diamond lattice expands at different rates, which may cause cracks to form in the diamond lattice structure and result in deterioration of the PCD. Damage is also due to the catalyzed formation of graphite at diamond-diamond necks at high temperatures, leading to loss of microstructural integrity and strength loss.
Attempts to address these issues have involved removing the catalyst or binder material from the diamond body after the PCD has been formed. Strong acid solutions have been used in some instances to remove or “leach” the catalyst or binder material from the diamond lattice structure. This approach has been practiced on the entire diamond body, where the catalyst material has been removed form the entire diamond body, or has been practiced on only part of or a region of the diamond body. Examples of “leaching” processes may be found, for example, in U.S. Pat. Nos. 4,288,248 and 4,104,344. In these instances, an acid solution, typically nitric acid or combinations of several acids (such as nitric and hydrofluoric acid) may be used to treat the diamond table, removing at least a portion of the catalyst or binder material PCD. By leaching out the catalyst material from the entire diamond body, thermally stable polycrystalline (TSP) diamond is formed. In certain embodiments, only a select portion or region of a diamond composite is leached, in order to gain thermal stability without losing impact resistance. As used herein, the term TSP is understood to include both of the above (i.e., partially and completely leached) compounds.
While conventional leaching processes with nitric/hydrofluoric acid mixtures are somewhat successful in removing the catalyst or binder material from the PCD, they tend to be time consuming, e.g., using mixtures of acids may easily take many weeks in order to leach out the catalyst or binder material. Further, the use and handling of acid solutions such as hydrofluoric acid presents potential safety, health, and environmental dangers. Still further, the use of such conventional leaching techniques presents certain limitations in the degree of catalyst and binder material, as well as other unwanted non-diamond materials, that may be removed from the PCD.
It is, therefore, desired that a technique and or materials be developed for the purpose of enhancing the process of removing unwanted catalyst or binder materials from the PCD. If is further desired that such technique and/or materials be engineered to also remove other unwanted non-diamond materials present in the PCD that may either contribute to undesired PCD performance properties and/or that may operate to impair subsequent processing of the PCD body after leaching.